The apparent affinity of human serum albumin (HSA) for divalent copper has long been the subject of great interest, due to its presumed role as the major Cu2+ -binding ligand in blood and cerebrospinal fluid. Using a combination of electronic absorption, circular dichroism and room-temperature electron paramagnetic resonance spectroscopies, together with potentiometric titrations, we competed the tripeptide GGH against HSA to reveal a conditional binding constant of log c =13.02±0.05 at pH 7.4. This rigorously determined value of the Cu2+ affinity has important implications for understanding the extracellular distribution of copper.
Keywords: affinity; amino-terminal copper and nickel (ATCUN) motif; copper; human serum albumin; metalloproteins.
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